Known biased electrochemical gas sensors typically require a prolonged stabilization time when powered up if the sensor, for example, has been left off load for a period of time. This is an issue for oxygen pump sensors, in particular, because oxygen sensors require power during normal operation since the target gas is usually present.
When known oxygen sensors are left unpowered, they no longer consume oxygen, and the oxygen builds up inside of the gas and liquid phase regions of the sensor, resulting in a large transient current upon power up. This process is described in U.S. application Ser. No. 12/754,023, which is assigned to the assignee hereof. The net result is that the sensor does not reach its optimum performance for a period of time after powering up.
For example, FIG. 1 is a graph 100 that illustrates the startup transient behavior of a known electrochemical oxygen pump sensor that has been off load for multiple days. Specifically, the graph 100 illustrates the stabilization time for such sensors that include a known potentiostat circuit, running on a +/−15V power supply, where the sensors are biased to a −600 mV vs internal platinum pseudo reference electrode, where the nominal sensor output is 400-500 μA in air, and where the sensors have been off load for multiple days.
Known potentiostat circuits often include a 10 Ohm resistor in series with the sensing electrode. For example, FIG. 2A is a circuit diagram of a known potentiostat circuit 200, FIG. 2B is a circuit diagram of a known current follower 210, and FIG. 2C is a circuit diagram of a circuit 220 approximately equivalent to a known electrochemical sensor.
FIG. 3 is a graph 300 that includes the data from the graph 100 plotted on a log scale. The data plotted on a log scale should illustrate a linear behavior if the transient current has a first order exponential decay. However, as seen in FIG. 3, linear behavior is only observed from about approximately 100-150 seconds and onwards by which time the error in air is already approximately 0.1-1% oxygen. Conversely, anomalous behavior is observed prior to 150 seconds even though the signal is saturated at approximately 40-100 seconds and then begins to decay.
In view of the above, there is a continuing, ongoing need for improved systems and methods of fast power up for electrochemical sensors.